2,2 :6 .2”-Terpyridine structure

FIGURE 17 Schematic formation of D3-symmetrical lanthanide triple-helical building blocks with (A) 2,6-dipicolinic acid and (B) 2,2 6, 2" terpyridine. Structures of the complexes [ 17(115 )3] and [Eu(L16%] + are redrawn from Harrowfield et al. (1995) and Semenova et al. (1999), respectively. 

Although there are many examples of diimine ligands tethered to organic chromophores, most compounds are based upon 2,2 -bipyridine and 2,2, 2"-terpyridine structures, the subject of other reviews in this series. Historically, (1) and its derivatives have been largely unexplored for... 

Kwong and Lee [39] prepared various chiral 2,2 6, 2"-terpyridines and tested them as copper ligands for the cyclopropanation of alkenes. High enantioselectivities were obtained, the presence of bulky alkyl groups at the 8-position of the tetrahydroquinoline ring being crucial (structure 29 in Scheme 17). Thus when = Bu, up to 90% ee for the trans and 94% for the cis isomer were obtained by performing the reaction at 0 °C (transIds = 69/31). 

Constable, E.C., Henney, R.P.G., Leese, T.A. and Tocher, D.A. (1990) Cyclometallation reactions of 6-phenyl-2,2 -bipyridine a potential C,N,N-donor analogue of 2,2 6, 2"-terpyridine. Crystal and molecular structure of dichlorobis (6-phenyl-2,2 -bipyridine)ruthenium(II). Journal of the Chemical Society, Dalton Transactions, (2), 443. 

Pitteri, B., Marangoni, G., Visentin, F., Bobbo, T., Bertolasi, V. and Gilli, P. (1999) Equilibrium and kinetic studies of (2,2 6, 2"-terpyridine)gold(III) complexes. Preparation and crystal structure of [Au(terpy)(0H)][C104]2. Journal of the Chemical Society, Dalton Transactions, (5), 677. 

E. C. Constable, B. Kariuki, and A. Mahmood, New approaches to sugar-functionalised 2,2 6, 2"-terpyridines based upon tetrafluorophenoxy spacers crystal and molecular structures of 4 -(tetrafluoro-4-hydroxyphenyl)-2,2 6, 2"-terpyridine and 4 -(4-methoxytetrafluorophenyl)-2, 2 6, 2" -terpyridine, Polyhedron, 22 (2003) 687-698. 

Fig. 26 (a) Structures of pyridine-, terpyridine-, and thiol-terminated PBI derivatives with different substituents at the bay positions X and X . The inset illustrates the alternation of optical properties of the PBIs with different bay-area substituents, (b) Plateau data-point histogram of Py-PBI in a mixture of mesitylene/THF (4 1). bias = 0.1 V, tip retraction rate was 60 nm s-1. The inset show the bias voltage dependence of the current through a molecular junction... 

Their activity compared to those of the Cu(II)-terpyridine and Cu(II)-bipyridine complexes indicate notable cooperativity between the metal centers (k mJ2 kmanoaet = 18-26 at pH = 7 and ca. 10 at the pH optimum of the given complex). The pH-rate profile of both complexes shows a bell-shaped structure. Thus, the postulated double general-base catalysis for both complexes is not fully justified. In case of 38 this was explained by possible inhibition by the buffer used. While double Lewis-acid activation is proposed for 37, single Lewis-acid activation is favored for 38. 

In contrast to 6-substituted-bipyridine systems such as 49, attachment of a five-membered heterocycle to the 2-position of 1,10-phenanthroline, which is a structural modification similar to the replacement of one of the terminal rings of terpyridine, does generally bring the ligand field into the crossover region and spin transitions have been observed for such systems when the heterocycle is thiazole 51 [74], imidazoline [75], triazole [76], pyrazole [77] and oxadiazole [78]. 

A complete description of the synthetic methodology and the characterization of the obtained metallosupramolecular block copolymers was reported in a recent paper [324]. These compounds have been referred to as metallosupramolecular block copolymers and designated by the acronym Ax-[Ru]-By, where A and B are the two different polymer blocks, -[Ru]- denotes the fczs-2,2/ 6/,2/terpyridine-ruthenium(II) linkage between the A and B blocks, and x and y represent the average degree of polymerization of the A and B blocks, respectively. The chemical structure of a PEB-[Ru]-PEO metallosupramolecular copolymer is depicted in Fig. 23. 

In most cases, metal ion coordination by a dendrimer takes place by units that are present along the dendrimer branches (e.g., amine, imine, or amide groups) or appended at the dendrimer periphery (e.g., terpyridine, cathecolamide ligands). When multiple identical coordinating units are present, dendrimers give rise to metal complexes of variable stoichiometry and unknown structures. Luminescent dendrimers with a well defined metal-coordinating site have been reported so far [16, 17], and the most used coordination site is 1,4,8,11-tetraazacyclotetradecane (cyclam). 

Finally, as far as the [Fen(terpy)2]2+ complex is concerned, its molecular structure is known. Its octahedral geometry is tetragonally distorted, in that the bond distance between the iron(II) ion and the central nitrogen atom of terpyridine is considerably shorter (Fe-N= 1.89 A) than the distance between theiron(II) ion and the two more external nitrogen atoms (Fe-N = 1.99 A).110... 

It has been mentioned previously that the formation of 2 1 Co 02 -peroxodimers is generally believed responsible for the irreversible coordination of dioxygen. In apparent contrast with this affirmation, the mixed bipyridine/terpyridine ligands complex [ Co(terpy)(bipy) 2 (fi-02)]4 +, the molecular structure of which is shown in Figure 16, constitutes an example of reversible coordination of the peroxo group.22... 

The spin state of iron(II) in substituted 2,2 6, 2"-terpyridine, (72), complexes depends on the position of bulky substituents—phenyl substituents in both the 6 and 6" positions give a high-spin complex phenyl substituents in the 4 and 6 positions give a complex which exists both in high-spin and in low-spin forms. Crystal structure determinations gave Fe—N bond distances in both forms of the 4,6-diphenyl complex and of the 6,6"-diphenyl complex. Each ligand in the latter com )lex has one terminal pyridine very weakly bonded to the iron, with... 

Phenylmethylsilanediol, synthesis, 42 155 Phenylsilanetriol, monosodium salts, 42 169 4 -Phenyl-2,2 6, 2 -terpyridine bis nickel complex, 30 74 molecular structure, 30 74 PhjtfluorenyllSiOH, 42 197 (Ph(Me2N)C-=Nli], 37 59-65 orientation of imino ligand, 37 61-63 (PhMe SiljCSiH OH, 42 244-245, 248 (PhMe SiljCsiMeHlOH), 42 191 Phosphaalkenes acyclic, 33 338-353 butadienes, 33 346-349 cumulenes, 33 352... 

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